Pancratic lens

ABSTRACT

The lens comprises a rear lens unit having a fixed focal length and a pancratic lens supplement having a variable magnification factor. The pancratic lens supplement comprises a stationary, positive first lens unit, an axially displaceable, negative second lens unit succeeding the first lens unit, an axially displaceable, positive third lens unit succeeding the second lens unit, and a stationary, negative fourth lens unit succeeding the third lens unit. The second and third lens units are adjustable to a first position, in which the lens has a smallest focal length fGmin, and to a second position in which said lens has a largest focal length fmax. The third lens unit has in both the first and second positions a magnification factor Beta 3 meeting the following conditions:

Umted State: y Lwub Gela et al.

1 PANCRATIC LENS [75] Inventors: Helmut Gela, Sudstadt; Trude Muszumanski, Vienna. both of Austria [731 Assignees: Karl Vockenhuber; Raimund Hauser, Vienna, Austria 22 Filed: Sept. 15, 1970 211 Appl. No.2 72,462

Primary ExaminerRonald l... Wibert Assistant ExaminerPaul A. Sacher Attorney-Ernest G. Montague [57] ABSTRACT The lens comprises a rear lens unit having a fixed 0/ Nov. 20, 1973 focal length and a pancratic lens supplement having a variable magnification factor. The pancratic lens sup-,

plement comprises a stationary, positive first lens unit, an axially displaceable, negative second lens unit succeeding the first lens unit, an axially displaceable, positive third lens unit succeeding the second lens unit, and a Stationary, negative fourth lens unit succeeding the third lens unit. The second and third lens units are adjustable to a first position, in which the lens has a smallest focal length f and to a second position in which said lens has a largest focal length f The third lens unit has in both the first and second positions a magnification factor B meeting the following conditions:

fflmin/ flll 3 -61! min fIImin/flll B21 ma: 2 1

4 Claims, 10 Drawing Figures hull PATENTEDHUYZO I975 I SHEET 1 BF 5 FIG./

PATENTEBnuvzo 191s SUFS F/GJO PANCRATIC LENS This invention relates to a pancratic lens, particularly for photographic purposes, which lens comprises a rear lens unit having a fixed focal length and a lens supplement having a variable magnification factor and comprising a stationary, positive lens unit facing the object, a stationary, negative lens unit facing the rear lens unit, and a negative lens unit and a positive lens unit disposed between said negative and positive stationary lens units.

It is an object of the invention to provide a pancratic lens which enables a formation of a satisfactory image of objects which are disposed within a range between infinity and a few millimeters before the foremost lens element of the lens and without need for auxiliary means such as supplementary lens elements. More particularly, the lens should be capable of forming images to a scale between 11 and l: so that the lens is suitable for taking photographs substantially in the macro range. Macrophotographs are considered photographs to a scale of 12-10 to l:l.

This object cannot be accomplished with the conventional close-up focusing effected by a displacement of the first lens unit of lenses of the described type because that displacement will not enable photographs of objects closer than about 1 meter.

A lens which is different in type from the one which has been disclosed hereinbefore can be focussed to very close objects by an axial displacement of inner lens units, which are disposed between a first lens unit and a rear lens unit. In .this way, image scales in the macro range may be obtained. On the other hand, the ratio of the smallest focal length to the largest one in the known lens is not higher than about 1:4.

In a lens which is of the type described first hereinbefore and which is not so restricted as to its zoom ratio, the object stated above is accomplished in that the magnification factor B, of the displaceable positive third lens unit meets the following conditions when the lens is set to the smallest overall focal length f and when the lens is set to the largest overall focal length fumefarm/ f!" "3:: min fGmln fIH B3 ma: z

wherein f, is the focal length of the third lens unit, and the two displaceable lens units are movable in two portions of their entire range of movement in accordance with two different functions, a displacement in accordance with the first function leavingin known manner the focal plane constant, whereas the displacement in accordance with the second function results also in known manner in an extreme variation of the distance from the object focal plane to the first lens unit.

If L is the distance from the image (13,) formed by the first lens unit to the image (8,) formed by the third lens unit, and d is the distance between the second and third lens units, it can be shown that the differential quotient dL/dd, disappears when the lens is set to the largest focal length f,,,,

This means that in that position the lens is entirely insensitive to a change of the distance between the second and third lens units. When the lens is set to the smallest focal length, an additional displacement of the third lens unit relative to the second lens unit is most effective to change L for a close-up focusing. As a result, the manufacture is not restricted to very small tolerances and the displacement required for a macro setting is so small that a substantial change of the state of correction of the lens is avoided.

It is another object of the invention to develop a more or less afocal pancratic lens supplement having a magnification range of about 1:8 and forming throughout the range of variation an image at a strictly constant position whereas simple optical and mechanical means are employed. Mechanically compensated pancratic systems are known, which involve only a relatively small expenditure of optical means and in which at least one functional group is displaced along the optical axis to produce a zoom efi'ect whereas a second functional group is displaced along the optical axis in response to the movement of the first-mentioned functional group so as to maintain the image in a constant position. This requirement involves a structure which is complicated and expensive. On the other hand, socalled optically compensated pancratic systems have been disclosed. L. Bergstein in his General Theory of Optically Compensated Pancratic Systems (Journal of the Optical Society of America, March, 1958) has shown that in a pancratic system of n stationary and displaceable functional groups arranged in alternation, with the displaceable functional groups being rigidly connected, the image is formed n times at the same position during the displacement of the movable functional groups. Whereas this solution involves comparatively simple and inexpensive mechanical means, it requires a large number of functional groups and yet the quality of the image formed by the optically compensated systems, even if they involve a considerable expenditure of optical means, is generally inferior to the quality of the image formed by mechanically compensated systems.

The Austrian Patent Specification No. 244,623 describes a pancratic system which is of a different type and which is a compromise between optically and mechanically compensated systems because its basic structure is similar to a certain extent to the translocators described by Gramatzki (Probleme der konstruktiven Optik, Berlin, 1957, pp. 116-118, as well as German Patent Specifications 622,046 and 676,946) whereas the image is maintained in a constant position in that the movement of the second displaceable functional group is moved in accordance with a slightly nonlinear function. The systems described by Gramatzki comprise four functional groups. The first of these groups is stationary and positive and is succeeded by a displaceable negative functional group. A positive functional group is moved in accordance with a linear function oppositely to the negative functional group and is succeeded by a negative stationary functional group. The magnification range is insufficient for present-day requirements. In the system disclosed in the German Patent Specification 676,946, the ratio of the largest magnification factor to the smallest one is 4:1. This range of 4:1 has been proved theoretically but can hardly be obtained in practice because the synthesis is based on infinitesimally thin lens elements and these must be replaced by complex functional groups comprising a plurality of lens elements in view of presentday requirements as to aperture and image field. The system according to the invention comprises also four functional groups, namely a positive stationary functional group facing the object, a negative stationary functional group, and a negative and a positive functional groups disposed between said stationary functional groups and adapted to be displaced in mutually opposite directions along the optical axis. The two displaceable lens units make approximately equal contributions to the change of the magnification factor. The latter property is typical of optically compensated pancratic systems.

When the third lens unit is displaced in linear dependence on the position of the second lens unit, the real intermediate image behind the third lens unit is formed twice at the same position during the change of the magnification factor. If the movement of the third lens unit is slightly corrected with the aid of simple mechanical means, the image formed by the substantially optically compensated pancratic system may be maintained strictly in a constant position with simple means throughout the magnification range. The compensating movement depends on the focal length of the third lens unit and may be represented as a second-order function.

It will also be possible, of course, to superimpose the correcting movement on the movement of the second lens unit.

The lens system described by way of example in the Austrian Patent Specification 244,623 has only a magnification range of 1:2 and it is an object of the invention to provide a magnification range of l to 8 or more.

This object is accomplished according to the invention in that a. the positive first lens unit consists in a known manner of a negative first lens component and a positive second lens component spaced from the first lens component, the negative lens component having a focal length of about 420%f, and the positive lens component having a focal length of about 90% f,, where f, is the overall focal length of the first lens unit, and the distance e between the associated principal points of the two lens components meets the requirement 0.7f, 2e 2035f,

b. the displaceable negative second lens unit consists of a negative meniscus component, which is convexly curved toward the light-receiving side, and consists of a biconvex lens element and a biconcave lens element cemented to the biconvex lens element, and of a bicon vex lens element having almost equal sides, and the refractive power (1),, 1 of the cemented component and the refractive power 4 of the biconcave lens element meet the following requirement:

c. the positive third lens unit consists of a biconvex lens component and a positive meniscus having approximately the same refractive power, and

d. the negative fourth lens unit consists of a single biconcave lens element having a less steeply curved surface which faces the third lens unit.

The invention will now be explained more fully with reference to some embodiments shown by way of example in the drawings, in which FIG. 1 shows the geometric arrangement of the lens when set to difierent focal lengths (positions I to V) and in close-up and macro settings (positions I to la).

FIGS. 2 to 5 illustrate four embodiments of cam grooves formed in a cylinder which encloses the lens and controlling the displacement of the second and third lens units. These cam grooves are shown in developed views.

FIGS. 6 to 8 are axial sectional views showing a lens according the invention in a wide-angle position (FIG.

6), tele position (FIG. 7) and macro position (FIG. 8).

FIGS. 9 and 10 show the state of correction of the lens when set to a given focal length, the lens being shown in FIG. 9 in infinity position and in FIG. 10 in macro position.

FIG. 1 shows the pancratic system diagrammatically represented by thin lens elements. In positions I to V, an image of an infinite object is formed in the film plane F. Position I corresponds to the smallest focal length f 7 millimeters (wide-angle position) and position V to the largest focal length f 56 millimeters (tele position). The second lens unit L, has in position I an image scale of l:0.347, which increases up to 11-1 in position V. The third lens unit L, has a similar function: its image scale ranges from l:-O.378 in position I to l:l in position V. As a result, an additional displacement of L; relative to L, is most effective in positions I and II but this effect decreases as the focal length increases and in position V the system is entirely insensitive to the additional displacement. This is significant for the mechanical adjustment of the entire lens because a small adjustment of the third lens unit L will change the wide-angle position and can be controlled to such an extent that it can be matched to the tele position, in which the lens has a very small response. On the other hand, the large response of the lens to a change of the distance between L, and L in positions I and II is essential for a focusing to very small object distances in the two wide-angle positions by a relatively small displacement of L,. If the lens units L, and L, were movable to change the image scale from 120.6 to l:-l.6, which change corresponds also to a magnification range of about 1:8, the desired result could not be achieved, as will be explained more fully hereinafter.

The first lens unit L produces an intermediate image B of an object. Although the first lens unit is positive, the intermediate image may be real or, if the object distance is very small, the intermediate image may be a virtual image. The second lens unit L, produces at B, a virtual image of the intermediate image 13 and the third lens unit L, produces a corresponding real image at 8,. L is the distance between B, and 13,. If the object distance and image distance for L, and L, are designated 0,, b, and a,, b;,, respectively, the following conditions will be met:

Several transformations and a differentiation of L for d,; give dL/ddg l fig In view of equation 4 dL/dd if :1

If a pancratic system is designed so that [3, equals -1 in the position for the largest focal length, that system will be entirely insensitive in the position to a change of the distance between L and L If L and L make approximately the same contributions to the change in focal length, the a L/dd will reach a maximum in the position for the smallest focal length, in accordance with equation 4. This effect should be utilized for a focusing in the macro range. Favorable conditions for the macro position will be obtained if the following conditions are met at the same time:

Baum:

The results which are due to the basic principle which has been discussed hereinbefore will now be shown with reference to a specific embodiment in which the focal length f of the first lens unit L 61.174

the focal length f: of the second lens unit L 15.l30 mm.,

the focal length f; of the third lens unit L +1 8.133

the focal length f, of the fourth lens unit L l9.579 mm.,

the focal length f of the fifth lens unit L +17.769

and in which the distance d, between L and L,, the distance d, between L, and L and the distance d, between L and L have in the discrete positions designated I to V in FIG. 1 the following values in millimeters:

I II III IV V d, 2.441 9.541 16.641 23.741 30.914 d 45.762 37.432 28.545 18.593 6.005 d 5.402 6.632 8.419 11.271 16.686 7.276 10.253 15.544 26.415 55.520 dL/dd 0.857 0.802 0.704 0.508 0 B, O.378 O.446 0.544 0.701 l.000

In the above table, the overall focal lengths f of the system in the respective positions are indicated in line 4 and the differential quotients a L/dd are indicated in line 5. The image distance b between the fifth lens unit L, and the film plane F is constant and amounts to 17.769 millimeters for an assumed object at a infinite distance.

If the differential quotient is replaced by the difference quotient and d, is changed by d 1 millimeter, the following near-point distances N will be obtained in the positions corresponding to differentfocal lengths:

III 462 I II 82 176 FIGS. 2 to 5 are developed views showing different cam cylinders for lens units 2 and 3. These cylinders are provided on the inside with substantially helical cam grooves, which are engaged by followers. These cam grooves and followers control the movement of the two displaceable lens units. FIG. 2 is a developed view showing a cam cylinder 1 provided with a cam groove 2 for the second lens unit and a cam groove 3 for the third lens unit. A pin 4 is secured to the barrel of the second lens unit and engages the cam groove 3. A pin5 is secured to the barrel of the third lens unit and guided in the cam groove 3. The pins 4 and 5 are shown in the associated cam grooves in a position corresponding to the wide-angle position of the lens. The cam groove 3 is continued by an axially directed extension groove 6, which includes an angle a with cam groove 3. A spring, not shown, urges the pin 5 against the righthand side of the cam groove 3. In the wide-angle position of the lens, the third lens unit can be axially displaced against the force of said spring so that the pin 5 can assume the position indicated in dotted lines at 50 and the system is then in a macro position for very near objects. FIG. 4 shows a modification of the cam mechanism just described. A cam groove 15 for the second lens unit is continued by an extension groove 16 having no lead. The cam groove 12 for the third lens unit is continued by an extension groove 13, which includes an obtuse angle with cam groove 12. During an adjustment of that lens barrel beyond the wide-angle range, the second lens unit is held in position whereas the third lens unit is axially displaced toward the second lens unit. FIG. 4 shows the pins 4 and 5 secured to the lens barrels of the second and third lens units, respectively, in the macro position.

The cam mechanisms shown in FIGS. 2 and 4 enable a macro setting in accordance with paragraph (a) above, FIG. 3 shows a cam cylinder for a macro setting in accordance with paragraph (b) above. Just as in FIG. 2, a pin 4 is guided in a cam groove 2 for the second lens unit. The cam groove 7 for the third lens unit is enlarged in the range of wide-angle positions. A spring, not shown, urges the pin 5 against the right-hand side of the cam groove. Different from the embodiment of FIG. 2, the embodiment shown in FIG. 5 enables a macro setting not only in the wide-angle range but also in a medium focal length range. A cam mechanism for adjustment within a macro range according to paragraph (c) above is shown in FIG. 5. Cam grooves 17 and 21 for the third and second lens units, respectively, are extended beyond the wide-angle range by converging portions. The two pins 4 and 5 secured to the barrels of lens units 2 and 3, respectively, are shown in the positions corresponding to the macro position of the system. This embodiment is similar to that of FIG. 4 in that the lens can be set for macrophotographs by a change of the focal length of the lens beyond the wideangle range.

The present embodiment is designed for Super 8 film and covers a focal length range from 7-56 millimeters and image scales from 1: to 11-5 so that it is adjustable substantially into the macro range, which is known to include image scales from 1:l0 to up to l:1. In the present case, an image of an object having a size of 27 20 millimeters may be formed in the full size of the frame of the Super 8 film.

The design of the lens according to the invention will now be explained more fully.

Lens unit L (r,r To ensure that the focal length of lens unit L is as short as possible, the lens unit L must be designed like a wide-angle lens having a backfocus which is larger than the focal length. This object can be accomplished in known manner in that the positive lens component of lens unit L, is preceded by a distinctly spaced apart negative lens component. In the present embodiment, the focal length of the positive lens component of lens unit L is about 90 percent, the focal length of the negative lens component is about 420 percent, and the distance e between the principal points of the two lens components is about 65 percent of the focal length of the entire lens unit L The distance e should meet the condition 0.7f, e 035f,

The negative lens component comprises a biconcave lens element and a biconvex lens element, which define between them a negative air meniscus, which is convex toward the light-receiving side and has radii of curvature meeting the condition The positive lens component consists of a biconvex lens element having equal sides and a positive meniscus, whose surfaces are convex toward the light-receiving side, and meets the condition wherein m, 1 and r, 2 are, respectively, the refractive powers of the biconvex lens element and the meniscus.

The biconvex lens element of the negative lens component consists of a glass for which v 40 and the two lens elements of the positive lens component consist of glass for which n 1.6

Lens unit L (r -r comprises a negative meniscus component, which is concavely curved towards the light-receiving side and consists of a biconvex lens element and a biconcave lens element cemented to the biconvex lens element, and the lens unit L, further comprises a biconcave lens element having almost equal sides. The following condition is met:

wherein 11 and 4m, are, respectively, the refractive powers of the cemented component and of the biconcave single lens element of lens unit L,. A correction of the spherical aberration and an anasticmatic field flatness are ensured because the following condition is met:

wherein 4m and 4a are, respectively, the refractive powers of the tenth and eleventh surfaces.

All three lens elements consist of a glass for which range but also for all object distances from infinity to a few millimeters before the foremost lens element vertex.

In the present embodiment of the invention, the lens.

wherein du and are, respectively, the refractive powers of the cemented lens component and of the sep arate meniscus.

Besides wherein 5 and m are, respectively, the refractive powers ofthe'fi'gative meniscus and of the biconvex lens element cemented thereto.

The design of the positive meniscus is defined by the inequa io 'l l 1sl l 27 i All three lens elements of lensml consist of glass for which Lens unit L (r -r is a single biconcave lens element and has a less steeply curved surface which faces the above-described lens unit L and which is related to the more steeply curved surface in accordance with the condition r lr l 5 r The single biconcave lens element L consists of a glass for which It is the function of lens unit L so to diverge a convergent bundle emerging from lens unit L that the bundle emerging from L is substantially parallel to the axis.

Lens unit L (r -r is the rear lens unit, which comprises in known manner four single lens elements and meets the condition zs u where d is the center thickness of the second lens element, which is biconcave and has equal sides, and d, and d, are respectively, the center distances of said second lens element from the preceding and succeeding positive lens elements.

The radii, distances and glass data of two specific embodiments are compiled in the two following Tables A and B. In these Tables and elsewhere in the specification and claims, r,, r,, r are in millimeters the radii of curvature of successive boundary surfaces of lens elements, d d d are in millimeters the center distances between successive boundary surfaces of lens elements, n nd n are the indices of refraction of media having center thicknesses d,, d,, d respectively, v v v are the Abbe numbers of lens elements having center thicknesses d,, d,, d f, is the focal length of the first lens unit, 4: and 4: are, re-

spectively, the refractive powers of the boundary surfaces having radii r and r o and 2' z are, respectively, the refractive powers of the biconvex lens element and of the meniscus of the positive lens component of the first lens unit, o and 5 are, respectively, the refractive powers of the cemented component and of the single biconcave lens element of the second lens unit, #111 and mu are, respectively, the refractive powers of the negative meniscus and of the biconvex lens element cemented to said meniscus in said third lens unit, em, and (p are, respectively, the refractive powers of the cemented lens component and of the separate meniscus of said third lens unit, and d) is the refractive power of said third lens unit.

Corresponding data for two specific embodiments of the rear lens unit are compiled in the two following tables C and D, in which r r r are in millimeters the radii of curvature of successive boundary surfaces of lens elements, d d (1,, are in millimeters the center distances between successive boundary surfaces of lens elements, ri m n are the indices of refraction of media having center thicknesses d d d respectively, v v v are the Abbe numbers of lens elements having center thicknesses d d d and fy is the focal length of said rear lens unit in millimeters.

The data compiled in Tables A, B, C, and D are subject to the following tolerances: For the curvature of individual surfaces up to a change of i1 0 percent of the refractive power of the respective lens unit, for the thicknesses up to a change of :10 percent of the focal length of the respective lens unit, for the refractive indices up to 10.03 and for the Abb'e numbers up to 15.

The pancratic lens supplements defined in Tables A and B may be respectively combined with the rear lens units defined in Tables C and D to provide pancratic lenses.

In each of these pancratic lenses, a plano-parallel glass prism is disposed between the pancratic lens supplement and the rear lens unit and has e.g. a thickness d 8.2 millimeters, an index of refraction n 1.569, an Abb number v 56.1; the distance d from the prism to the rearmost lens element vertex of the lens supplement is 1.9 millimeters and the distance d from the prism to the foremost lens element vertex of the rear lens unit is 5.05 millimeters.

The two pancratic lenses defined above by way of example have a smallest focal length f 7 millimeters and a largest focal length fnmz 56 millimeters.

The relative aperture is l:l.8. The shortest distance of an object from the foremost lens element vertex is s 9.48 millimeters.

The states of correction for the infinity and macro positions are apparent from FIGS. 9 and 10.

What is claimed is:

1. A pancratic lens supplement having a continuously variable magnification factor and designed like a Galilean telescope,

said pancratic lens supplement comprising a stationary, positive first lens unit, an axially displaceable, negative second lens unit succeeding said first lens unit, an axially displaceable, positive third lens unit succeeding said second lens unit, and a stationary, negative fourth lens unit succeeding said third lens unit,

said first lens unit consisting of a negative first lens component and a positive second lens component spaced behind said first lens component,

said first and second lens components having focal lengths of about 420%f, and about 9096]}, respectively, where f, is the focal length of said first lens unit,

said second lens unit consisting of third and fourth lens components,

said third lens component consisting of a negative meniscus convexly curved toward the lightreceiving side and consisting of a biconvex lens element and a biconcave lens element cemented to said biconvex lens element,

said fourth lens component consisting of a biconcave lens element having almost equal sides,

said third lens unit consisting of a biconvex lens component and a positive meniscus having about the same refractive power,

said fourth lens unit consisting of a single biconcave lens element having a less steeply curved surface facing said third lens unit,

said first lens component consists of a biconcave lens element and a biconvex lens element, which define between them a rearwardly concave, negative air meniscus,

said second lens component consists of a biconvex lens element having equal sides and a positive meniscus having rearwardly concave surfaces and said biconvex lens component of said third lens unit consists of a negative meniscus which is convexly curved toward said second lens unit and a biconvex lens element having substantially equal sides and which has the following data:

wherein r r,,

r are in millimeters the radii of of said third lens component, 115, and 4 .are, respectively, the refractive powers of the biconvex lens element and of the meniscus of said second lens component, 4),, i and 45 are, respectively, the refractive powers of said third andfourth lens components, wherein d1, m and dz are, respectively, the refractive powers of said meniscus and said biconvex lens element of said biconvex lens component, qb ml and are, respectively, the refractive powers of said biconvex lens component and said positive meniscus of said third lens unit, and 4m, is the refractive power of said third lens unit.

2. A pancratic lens supplement having a continuously variable magnification factor and designed like a Galilean telescope,

said pancratic lens supplement comprising a stationary, positive first lens unit, an axially displaceable, negative second lens unit succeeding said first lens unit, an axially displaceable, positive third lens unit succeeding said second lens unit, and a stationary, negative fourth lens unit succeeding said third lens unit,

said first lens unit consisting of a negative first lens component and a positive second lens component spaced behind said first lens component,

said first and second lens components having focal lengths of about -420%f, and about 9096]}, respec tively, where f, is the focal length of said first lens unit,

said second lens unit consisting of third and fourth lens components,

said third lens component consisting of a negative meniscus convexly curved toward the lightreceiving side and consisting of a biconvex lens element and a biconcave lens element cemented to said biconvex lens element,

said fourth lens component consisting of a biconcave lens element having almost equal sides,

said third lens unit consisting of a biconvex lens component and a positive meniscus having about the same refractive power,

said fourth lens unit consisting of a single biconcave lens element having a less steeply curved surface facing said third lens unit,

said first lens component consists of a biconcave lens element and a biconvex lens element, which define between them a rearwardly concave, negative air meniscus,

said second lens component consists of a biconvex lens element having equal sides and a positive meniscus having rearwardly concave surfaces and said biconvex lens component of said third lens unit consists of a negative meniscus which is convexly curved toward said second lens unit and a biconvex lens element having substantially equal sides and which has the following data:

wherein r,, r r, are in millimeters the radii of curvature of successive boundary surfaces of lens elements, d d d are in millimeters the center distances between successive boundary surfaces of lens elements, n n m are the indices of refraction of media having center thicknesses d d d respectively, v v v are the Abbe numbers of lens elements having center thicknesses d d d f, is the focal length of the first lens unit, qS and 4) are, respectively, the refractive powers of the forward and rear surfaces of said biconvex lens element of said third lens component, (1), and (1), are, respectively, the refractive powers of said second lens component, do and 4: are, respectively, the refractive powers of said third and fourth lens components, wherein rim, and m are, respectively, the refractive powers of said meniscus and said biconvex lens element of said biconvex lens component, 4a, and 4m, 2 are, respectively, the refractive powers of said biconvex lens component and said positive meniscus of said third lens unit, and 11 is the refractive power of said third lens unit. 3. A pancratic lens, which comprises a rear lens unit having a fixed focal length and a pancratic lens supplement having a continuously variable magnification factor and designed like a Galilean telescope, said pancratic lens supplement comprising a stationary, positive first lens unit, an axially displaceable, negative second lens unit succeeding said first lens unit, an axially displaceable, positive third lens unit succeeding said second lens unit and a stationary, negative fourth lens unit succeeding said third lens unit, said first lens unit consisting of a negative first lens component and a positive second lens component spaced behind said first lens component, said first and second lens components having focal lengths of about -420% f, and about 9096]}, respectively, where f, is the focal length of said first lens unit, said second lens unit consisting of third and fourth lens components, said third lens component consisting of a negative meniscus convexly curved toward the lightreceiving side and consisting of a biconvex lens element and a biconcave lens element cemented to said biconvex lens element, said fourth lens component consisting of a biconcave lens element having almost equal sides,

said third lens unit consisting of a biconvex lens component and a positive meniscus having about the same refractive power,

said fourth lens unit consisting of a single biconcave lens element having a less steeply curved surface facing said third lens unit, said second and third lens units being adjustable to a first position in which said lens has a smallest focal length f and to a second position in which said lens has a largest focal length f said pancratic lens supplement further comprising means for displacing said second and third lens units to said first and second positions through a first range in accordance with a first function selected to maintain the object focal plane of the lens constant and through a second range in accordance with a second function selected to vary the distance from the object focal plane to said first lens unit, said rear lens unit constitutes an extended triplet consisting of a biconvex lens element, a biconcave lens element and two positive single lens elements, said biconcave lens element of said rear lens unit has equal sides and meets the condition: 24 25 m wherein di is the center thickness of said biconcave lens element and (1, and d are the vertex distances from said biconcave lens element to adjacent lens elements, said rear lens unit has the following data:

in which r r r are in millimeters the radii of curvature of successive boundary surfaces of lens elements, (1 d d are in millimeters the center distances between successive boundary surfaces of lens elements, u u 71 are the indices of refraction of media having center thicknesses d d :1 respectively, v v v are the Abb numbers of lens elements having center thicknesses d d d and fy is the focal length of said rear lens unit in millimeters. 4. A pancratic lens, which comprises a rear lens unit having a fixed focal length and a pancratic lens supplement having a continuously variable magnification factor and designed like a Galilean telescope, said pancratic lens supplement comprising a stationary, positive first lens unit, an axially displaceable, negative second lens unit succeeding said first lens unit, an axially displaceable, positive third lens unit succeeding said second lens unit, and a stationary, negative fourth lens unit succeeding said third lens unit, said first lens unit consisting of a negative first lens component and a positive second lens component spaced behind said first lens component, said first and second lens components having focal lengths of about 420%f, and about respectively, where f, is the focal length of said first lens unit,

said second lens unit consisting of third and fourth lens components,

said third lens component consisting of a negative meniscus convexly curved toward the lightreceiving side and consisting of a biconvex lens element and a biconcave lens element cemented to said biconvex lens element,

said fourth lens component consisting of a biconcave lens element having almost equal sides,

said third lens unit consisting of a biconvex lens component and a positive meniscus having about the same refractive power,

said fourth lens unit consisting of a single biconcave lens element having a less steeply curved surface facing said third lens unit,

said second and third lens units being adjustable to a first position in which said lens has a smallest focal length f and to a second position in which said lens has a largest focal length f said pancratic lens supplement further comprising means for displacing said second and third lens units to said first and second positions through a first range in accordance with a first function selected to maintain the object focal plane of the lens constant and through a second range in accordance with a second function selected to vary the distance from the object focal plane to said first lens unit,

said rear lens unit constitutes an extended triplet consisting of a biconvex lens element, a biconcave lens element and two positive single lens elements, said biconcave lens element of said rear lens unit has equal sides and meets the condition:

wherein d is the center thickness of said biconcave lens element and d, and d, are the vertex distances from said biconcave lens element to adjacent lens elements,

in which r r r are in millimeters the radii of v are the Abbe numbers of lens elements having center thicknesses d d d and f is the focal length of said rear lens unit in millimeters. 

1. A pancratic lens supplement having a continuously variable magnification factor and designed like a Galilean telescope, said pancratic lens supplement comprising a stationary, positive first lens unit, an axially displaceable, negative second lens unit succeeding said first lens unit, an axially displaceable, positive third lens unit succeeding said second lens unit, and a stationary, negative fourth lens unit succeeding said third lens unit, said first lens unit consisting of a negative first lens component and a positive second lens component spaced behind said first lens component, said first and second lens components having focal lengths of about -420%fI and about 90%fI, respectively, where fI is the focal length of said first lens unit, said second lens unit consisting of third and fourth lens components, said third lens component consisting of a negative meniscus convexly curved toward the light-receiving side and consisting of a biconvex lens element and a biconcave lens element cemented to said biconvex lens element, said fourth lens component consisting of a biconcave lens element having almost equal sides, said third lens unit consisting of a biconvex lens component anD a positive meniscus having about the same refractive power, said fourth lens unit consisting of a single biconcave lens element having a less steeply curved surface facing said third lens unit, said first lens component consists of a biconcave lens element and a biconvex lens element, which define between them a rearwardly concave, negative air meniscus, said second lens component consists of a biconvex lens element having equal sides and a positive meniscus having rearwardly concave surfaces and said biconvex lens component of said third lens unit consists of a negative meniscus which is convexly curved toward said second lens unit and a biconvex lens element having substantially equal sides and which has the following data: r1-67.2 d1 1.9/nd1 1.805 vd1 25.4 r2+105 d2 1.9 r3+116 d3 8.3/nd3 1.574 vd3 56.4 r4-60.8 d4 4.9 r5+187 d5 4.4/nd5 1.643 vd5 48.0 r6-187 d6 0.1 r7+45.4 d7 5.7/nd7 1.658 vd7 50.9 r8+166 d8 0.8/nd8 -29.3 r9+93.2 d9 3.8/nd9 1.805 vd9 25.4 r10-52.2 d10 1.0/nd10 1.620 vd10 60.3 phi 10 0.00354 r11+16.6 d11 4.9 phi 11 -0.03746 r12-37.9 d12 1.0/nd12 1.744 vd12 44.8 r13+41.2 d13 41.8/nd13 -2.0 r14+77.7 d14 0.8/nd14 1.741 vd14 27.6 r15+30.0 d15 3.8/nd15 1.652 vd15 44.9 r16-30.0 d16 0.1 r17+19.9 d17 2.7/nd17 1.720 vd17 50.4 r18+78.2 d18 2.8/nd18 -14.1 r19-41.1 d19 0.9/nd19 1.620 vd19 60.3 r20+17.4 fI 61.174 phi I 0.00686 phi I 0.01074 phi II 0.02493 phi II -0.03789 phi III -0.01499 phi III 0.02787 phi III 0.04230 phi III 0.05515 phi III 0.02749 wherein r1, r2, ... r20 are in millimeters the radii of curvature of successive boundary surfaces of lens elements, d1, d2, ... d19 are in millimeters the center distances between successive boundary surfaces of lens elements, nd1, nd3, ... nd19 are the indices of refraction of media having center thicknesses d1, d3, ... d19, respectively, vd1, vd3, ... vd19 are the Abbe numbers of lens elements having center thicknesses d1, d3, ... d19, fI is the focal length of the first lens unit, phi 10 and phi 11 are, respectively, the refractive powers of the forward and rear surfaces of said biconvex lens element of said third lens component, phi I and phi I are, respectively, the refractive powers of the biconvex lens element and of the meniscus of said second lens component, phi II and phi II are, respectively, the refractive powers of said third and fourth lens components, wherein phi III and phi III are, Respectively, the refractive powers of said meniscus and said biconvex lens element of said biconvex lens component, phi III and phi III are, respectively, the refractive powers of said biconvex lens component and said positive meniscus of said third lens unit, and phi III is the refractive power of said third lens unit.
 2. A pancratic lens supplement having a continuously variable magnification factor and designed like a Galilean telescope, said pancratic lens supplement comprising a stationary, positive first lens unit, an axially displaceable, negative second lens unit succeeding said first lens unit, an axially displaceable, positive third lens unit succeeding said second lens unit, and a stationary, negative fourth lens unit succeeding said third lens unit, said first lens unit consisting of a negative first lens component and a positive second lens component spaced behind said first lens component, said first and second lens components having focal lengths of about -420%fI and about 90%fI, respectively, where fI is the focal length of said first lens unit, said second lens unit consisting of third and fourth lens components, said third lens component consisting of a negative meniscus convexly curved toward the light-receiving side and consisting of a biconvex lens element and a biconcave lens element cemented to said biconvex lens element, said fourth lens component consisting of a biconcave lens element having almost equal sides, said third lens unit consisting of a biconvex lens component and a positive meniscus having about the same refractive power, said fourth lens unit consisting of a single biconcave lens element having a less steeply curved surface facing said third lens unit, said first lens component consists of a biconcave lens element and a biconvex lens element, which define between them a rearwardly concave, negative air meniscus, said second lens component consists of a biconvex lens element having equal sides and a positive meniscus having rearwardly concave surfaces and said biconvex lens component of said third lens unit consists of a negative meniscus which is convexly curved toward said second lens unit and a biconvex lens element having substantially equal sides and which has the following data: r1-67.2 d1 1.9/nd1 1.805 vd1 25.4 r2+105 d2 1.9 r3+116 d3 8.3/nd3 1.574 vd3 56.4 r4-60.8 d4 4.9 r5+187 d5 4.4/nd5 1.643 vd5 48.0 r6-187 d6 0.1 r7+45.4 d7 5.7/nd7 1.658 vd7 50.9 r8+166 d8 0.8/nd8 -29.3 r9+93.2 d9 3.8/nd9 1.805 vd9 25.4 r10-52.2 d10 1.0/nd10 1.620 vd10 60.3 phi 10 0.00354 r11+16.6 d11 4.9 phi 11 -0.03746 r12-37.9 d12 1.0/nd12 1.744 vd12 44.8 r13+41.2 d13 41.8/nd13 -2.0 r14+77.7 d14 0.8/nd14 1.741 vd14 27.6 r15+30.0 d15 3.8/nd15 1.652 vd15 44.9 r16-30.0 d16 0.1 r17+19.9 d17 2.7/nd17 1.717 vd17 48.0 r18+78.7 d18 2.8/nd18 -14.1 r19-40.0 d19 0.9/nd19 1.620 vd19 60.3 r20+17.6 fI 61.174 phi I 0.00686 phi I 0.01074 phi II -0.02493 phi II -0.03789 phi III -0.01499 phi III 0.02787 phi III 0.04230 phi III 0.05515 phi III 0.02749 wherein r1, r2, ... r20 are in millimeters the radii of curvature of successive boundary surfaces of lens elements, d1, d2, ... d19 are in millimeters the center distances between successive boundary surfaces of lens elements, nd1, nd3, ... nd19 are the indices of refraction of media having center thicknesses d1, d3, ... d19, respectively, vd1, vd3, ... vd19 are the Abbe numbers of lens elements having center thicknesses d1, d3, ... d19, fI is the focal length of the first lens unit, phi 10 and phi 11 are, respectively, the refractive powers of the forward and rear surfaces of said biconvex lens element of said third lens component, phi I and phi I are, respectively, the refractive powers of said second lens component, phi II and phi II are, respectively, the refractive powers of said third and fourth lens components, wherein phi III and phi III are, respectively, the refractive powers of said meniscus and said biconvex lens element of said biconvex lens component, phi III and phi III are, respectively, the refractive powers of said biconvex lens component and said positive meniscus of said third lens unit, and phi III is the refractive power of said third lens unit.
 3. A pancratic lens, which comprises a rear lens unit having a fixed focal length and a pancratic lens supplement having a continuously variable magnification factor and designed like a Galilean telescope, said pancratic lens supplement comprising a stationary, positive first lens unit, an axially displaceable, negative second lens unit succeeding said first lens unit, an axially displaceable, positive third lens unit succeeding said second lens unit and a stationary, negative fourth lens unit succeeding said third lens unit, said first lens unit consisting of a negative first lens component and a positive second lens component spaced behind said first lens component, said first and second lens components having focal lengths of about -420%fI and about 90%fI, respectively, where fI is the focal length of said first lens unit, said second lens unit consisting of third and fourth lens components, said third lens component consisting of a negative meniscus convexly curved toward the light-receiving side and consisting of a biconvex lens element and a biconcave lens element cemented to said biconvex lens element, said fourth lens component consisting of a biconcave lens element having almost equal sides, said third lens unit consisting of a biconvex lens component and a positive meniscus having about the same refractive power, said fourth lens unit consisting of a single biconcave lens element having a less steeply curved surface facing said third lens unit, said second and third lens units being adjustable to a first position in which said lens has a smallest focal length fmin, and to a second position in which said lens has a largest focal length fmax, said pancratic lens supplement further comprising means for displacing said second and third lens units to said first and second positions through a first range in accordance with a first function selected to maintain the object focal plane of the lens constant anD through a second range in accordance with a second function selected to vary the distance from the object focal plane to said first lens unit, said rear lens unit constitutes an extended triplet consisting of a biconvex lens element, a biconcave lens element and two positive single lens elements, said biconcave lens element of said rear lens unit has equal sides and meets the condition: d24>d25>d26 wherein d25 is the center thickness of said biconcave lens element and d24 and d26 are the vertex distances from said biconcave lens element to adjacent lens elements, said rear lens unit has the following data: r23+17.8 d23 4.2/nd23 1.570 vd23 49.5 r24-49.7 d24 3.5 r25-16.5 d25 2.4/nd25 1.847 vd25 23.8 fV 17.769 r26+16.5 d26 1.35 r27-585 d27 3.8/nd27 1.569 vd27 63.1 r28-12.4 d28 0.2 r29+18.9 d29 3.1/nd29 1.620 vd29 60.3 r30-23.3 in which r23, r24, ... r30 are in millimeters the radii of curvature of successive boundary surfaces of lens elements, d23, d25, ... d29 are in millimeters the center distances between successive boundary surfaces of lens elements, nd23, nd25, ... nd29 are the indices of refraction of media having center thicknesses d23, d25, ... d29, respectively, vd23, vd25, ... vd29 are the Abbe numbers of lens elements having center thicknesses d23, d25, ... d29 and fV is the focal length of said rear lens unit in millimeters.
 4. A pancratic lens, which comprises a rear lens unit having a fixed focal length and a pancratic lens supplement having a continuously variable magnification factor and designed like a Galilean telescope, said pancratic lens supplement comprising a stationary, positive first lens unit, an axially displaceable, negative second lens unit succeeding said first lens unit, an axially displaceable, positive third lens unit succeeding said second lens unit, and a stationary, negative fourth lens unit succeeding said third lens unit, said first lens unit consisting of a negative first lens component and a positive second lens component spaced behind said first lens component, said first and second lens components having focal lengths of about -420%fI and about 90%fI, respectively, where fI is the focal length of said first lens unit, said second lens unit consisting of third and fourth lens components, said third lens component consisting of a negative meniscus convexly curved toward the light-receiving side and consisting of a biconvex lens element and a biconcave lens element cemented to said biconvex lens element, said fourth lens component consisting of a biconcave lens element having almost equal sides, said third lens unit consisting of a biconvex lens component and a positive meniscus having about the same refractive power, said fourth lens unit consisting of a single biconcave lens element having a less steeply curved surface facing said third lens unit, said second and third lens units being adjustable to a first position in which said lens has a smallest focal length fmin, and to a second position in which said lens has a largest focal length fmax, said pancratic lens supplement further comprising means for displacing said second and third lens units to said first and second positions through a first range in accordance with a first function selected to maintain the object focal plane of the lens constant and through a second range in accordance with a second function selected to vary the distance from the object focal plane to said first lens unit, said rear lens unit constitutes an extended triplet consisting of a biconvex lens element, a biconcave lens element and two positive single lens elements, said biconcave lens element of said rear lens unit has equal sides and meets the condition: d24>d25>d26 wherein d25 is the center thickness of said biconcave lens element and d24 and d26 are the vertex distances from said biconcave lens element to adjacent lens elements, r23+20.0 d23 4.2/nd23 1.569 vd23 56.1 r24-49.7 d24 3.5 r25-19.1 d25 2.8/nd25 1.847 vd25 23.8 r26+19.1 d26 1.35 r27-585 d273.8/nd27 1.569 vd27 63.1 r28-12.4 d28 0.2 r29+16.4 d29 3.1/nd29 1.641 vd29 60.1 r30-45.9 in which r23, r24, ... r30 are in millimeters the radii of curvature of successive boundary surfaces of lens elements, d23, d25, ... d29 are in millimeters the center distances between successive boundary surfaces of lens elements, nd23, nd25, ... nd29 are the indices of refraction of media having center thicknesses d23, d25, ... d29, respectively, vd23, vd25, ... vd29 are the Abbe numbers of lens elements having center thicknesses d23, d25, ... d29 and fV is the focal length of said rear lens unit in millimeters. 